Former Manchester United captain Gary Neville believes Cristiano Ronaldo's body language could become a problem.
He has urged manager Ole Gunnar Solskjaer to tell Ronaldo to keep his frustrations behind closed doors in future.
Ronaldo started Saturday's 1-1 draw at Old Trafford among the substitutes and couldn't inspire United to victory when introduced during the second half.
At the final whistle, the Portuguese star looked visibly angry as he walked straight back to the dressing room muttering to himself.
Speaking on Sky Sports, Neville said: "I watched him walk off and I can't say I like it.
"Is Cristiano upset when he doesn't play? Yes. Is Cristiano upset when he doesn't score? Yes. Is Cristiano annoyed as hell when the team don't win? Of course.
"We know those things. He doesn't have to prove that.
"He walked off the pitch muttering to himself, which throws the questions up in the air - what's he saying? Who is he annoyed with?
"It can only come back to the manager. Actions like that - and Cristiano is smart enough to know this - will bring real pressure on the manager, more pressure than Ole Gunnar Solskjaer is already under.
"I think that is something that just has to be managed in the next couple of months. Cristiano is not always going to score, he's maybe not going to play every single game.
"But I think if he walks off like that, it's going to put immense pressure on Solskjaer. There's no doubt the talk after the game was about the manager.
"He has this collection of players but they haven't got this style of play, they haven't got this or that. He didn't pick Ronaldo..."
Need a VPN? Or seeking to switch? Then support Tribal Football by clicking here to sign up with our official partners NordVPN. Not only will you receive the best VPN experience, but also great discounts by signing up via Tribal Football. Thanks for your support!